Method and apparatus for cutting steel to reduce slag adherence

ABSTRACT

A steel cutting apparatus includes a cutting torch that is moved in an arcuate path for guiding the cutting torch so that a cutting flame of the cutting torch is always aimed at a bottom corner of the steel at the side where the cutting process begins. Molten steel and iron oxide flow through a kerf in the steel toward the bottom corner, and drop away from the billet for collection and disposal. Only a very small amount of slag adheres to the bottom corner of the billet when cutting is complete.

This application is a division of application Ser. No. 09/934,701, filedAug. 22, 2001 now U.S. Pat. No. 6,663,824.

FIELD OF THE INVENTION

The present invention relates to a process for separation ofmetallurgical products, such as steel billets, blooms or small slabs,and more particularly to the cutting of these products into selectedlengths, while reducing the adherence of slag on cut edges of theproducts.

BACKGROUND OF THE INVENTION

In a continuous casting operation, a continuous cast strand is cut intolengths, such as steel billets, using an oxygen-fuel cutting torchsystem. Oxygen-fuel cutting torch systems are well known and arecommonly used in the cutting and welding industry. A cutting torch ismounted to move with the cast steel strand and to make a lateralseparating cut through the strand perpendicular to its longitudinal axisand its direction of movement.

Conventionally, the cutting torch is positioned above and moveslongitudinally together with the steel strand while being driven in astraight path transverse to the steel strand. Thus, the cutting torchflame projects downwardly and is moved horizontally across the steelstrand, thereby cutting the billet. During the cutting process, thecutting torch flame produces a kerf in the steel strand. Molten steeland iron oxide flow downwardly through the kerf and drop below thebillet for collection and disposal. However, some of the molten steeland iron oxide adhere to the bottom edges of the kerf and form slagbeads that accumulate along those edges. This slag must be removed;otherwise it adversely affects subsequent forming operations performedon the billets, which may cause defects in finished steel products madefrom the billets. For example, the slag beads may adhere to rollersurfaces used for steel plate forming. Since the slag beads are muchharder than the steel billet, the slag beads may form dimples in therolled steel surface, or embed in the surface. However, removing theslag beads from the billet in a secondary operation, such as scarfing,is tedious, time consuming and costly. Therefore, efforts are generallymade to immediately remove the slag accumulation during the cuttingprocess.

In general, it has been discovered, and is well known that directing afluid stream at the molten slag as it forms on the edges of the kerftends to blow it away and thereby reduce its adherence. The fluid streammay comprise air, oxygen, water, mixtures thereof, or other gases orliquids. U.S. Pat. No. 4,336,078, entitled PROCESS AND APPARATUS FOR THESEPARATION OF METALLURGICAL PRODUCTS, issued to Radtke on Jun. 22, 1982,for example, describes process and apparatus for separatingmetallurgical products such as ingots, slabs or plate-shaped work piecesusing a cutting torch deposed on one side of the product. The cuttingtorch follows a prescribed cutting line and forms a front cutting edgeon the surface of the product facing the cutting torch, a rear cuttingedge on the opposite side of the product, and a cutting jointtherebetween. At least one gaseous jet is directed at the rear cuttingedge of the product to blow away molten metal and liquid slag from therear cutting edge during the cutting process, thereby preventing theformation of slag beads at the edges of the cutting joint.

As another example of the slag adherence reduction, U.S. Pat. No.4,923,527, entitled APPARATUS AND METHOD FOR SLAG-FREE CUING OF BILLETSAND THE LIKE, issued to Ludwigson on May 8, 1990, describes a billetcutting apparatus of the type, which includes an oxy-fuel cutting torch.The apparatus includes a slag removal nozzle operative simultaneouslywith the cutting torch to direct a jet of oxygen along the lower edge ofthe billet to remove slag beads tending to form thereon. The oxygennozzle has a unique opening configuration, which provides a thin, flatoxygen stream effective over a substantial distance, such that thenozzle can be mounted laterally of the billet and outside the hostileand potentially damaging environment created by the cutting torch andthe hot billet. The oxygen nozzle may be conveniently mounted in a fixedposition, and in an automated billet cutting apparatus, may be attacheddirectly to one of the billet clamping arms.

Neither of these methods has achieved wide commercial success, however.Consequently, there is still a need for alternative technologies tominimize slag bead adherence during the cutting of steel billets, andthe like.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a method andapparatus for cutting steel with a cutting torch, while reducing slagadherence to a cut edge of the steel.

It is another object of the invention to provide a method and apparatusfor cutting steel, which minimizes slag formation by moving a cuttingtorch in an arcuate path to reduce the area where slag can accumulate onthe cut edges.

In accordance with one aspect of the present invention, a method isprovided for cutting steel with a cutting torch to reduce slag adherenceto a cut edge of the steel. The method comprises steps of commencing acut at a first side of the steel, and moving the cutting torch in aarcuate path shaped to continuously aim a cutting flame at a fixed pointlocated at a bottom of a first side of the steel, and following thearcuate path to keep the cutting flame aimed at the fixed point untilthe steel is cut.

When the steel has a bottom surface and an angle of the bottom corner atthe first side is not greater than 90°, it is preferable to move thecutting torch from the first side of the steel to a second side which isopposite the first side, while gradually rotating the cutting torch froma first orientation perpendicular to the bottom surface, and along thearcuate path to a second orientation parallel to the bottom surface ofthe steel, so that the cutting flame of the cutting torch iscontinuously aimed at the bottom corner of the first side of the steel.The cutting torch is preferably moved transversely relative to the steelwhile-being maintained stationary relative to a longitudinal axis of thesteel. In particular, in continuous cast cutting operations, the cuttingtorch is moved synchronously with the steel in a direction parallel withthe longitudinal axis of the steel. Thus, the molten metal and ironoxide, under the influence of the force of the cutting flame jet, flowtoward the bottom corner at the first side of the steel as the cuttingtorch moves along the arcuate path and the cutting flame thereby pivotsacross the steel. Substantially all of the molten metal and iron oxidedrop off below the steel, and only a very small amount of slag beadadheres to the bottom corner of the first side of the steel, which cangenerally be ignored in a subsequent forming process.

in accordance with another aspect of the invention, an apparatus isprovided for cutting steel to reduce slag adherence to the steel. Theapparatus comprises a cutting torch and means for moving the cuttingtorch in an arcuate path to ensure that a cutting flame of the cuttingtorch is always aimed at a bottom corner of the steel.

The means for moving the cutting torch preferably comprises a trackforming the arcuate path for guiding the cutting torch movement, a drivemechanism operatively connected to the cutting torch to move the cuttingtorch along the track, and a frame to support the track and the drivemechanism. A linkage system is preferably included in the drivemechanism to convert a rotational movement of a rotating shaft into themovement of the cutting torch along the track.

In one embodiment of the present invention, a sleeve having internalthreads is rotatably connected to the cutting torch about an axisperpendicular to both a plane determined by the track and a longitudinalaxis of the sleeve. A drive shaft is provided which has a free end andan end connected by means of a universal joint, to the rotating shaft.The drive shaft has external threads that threadingly engage the sleeve.The drive shaft is pivotable about an axis perpendicular to the plane ofthe track and extends through the universal joint. Thus, when therotating shaft rotates the drive shaft through the universal joint, thesleeve moves along the drive shaft and causes the cutting torch to movealong the track. The drive shaft may be rotated by a motor mounted tothe frame.

The frame may be movable along a path parallel to the longitudinal axisof the steel and include clamping means for releasably clamping thesteel between the frames in a position in which a longitudinal axis ofthe steel is perpendicular to the plane determined by the track. Thusthe cutting torch is moved together with the steel when, for example,the steel is a continuous cast strand exiting a caster.

In another embodiment of the invention, a rack and a pinion are providedto replace the motor for converting the movement of the frame into therotational movement of the rotating shaft. The rotating shaft in turnrotates the drive shaft through the universal joint, thereby causing thecutting torch to move along the track. The rack is mounted to astationary support, such as a track for supporting and guiding themovable frame. The pinion is affixed to the rotating shaft and isadapted to rotate together with the rotating shaft, which is rotatablymounted to the frame.

In accordance with a further embodiment of the invention, a doubleacting fluid cylinder and pivoting linkage system serve as the drivemechanism. The cylinder is pivotally mounted to the frame about an axisperpendicular to the plane of the track and is also pivotally connectedto the cutting torch about an axis, which is also perpendicular to theplane of the track. Therefore, the cylinder pivots about its mountingaxis and the cutting torch is urged along the track when the cylinder isoperated in either direction.

The present invention advantageously provides an alternative technologyfor cutting steel with a cutting using a secondary nozzle to inject afluid stream for slag bead removal.

Other advantages and features of the present invention will be betterunderstood with reference to preferred embodiments of the presentinvention described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus generally described the nature of the present invention,reference will now be made to the accompanying drawings, showing by wayof illustration the preferred embodiments thereof, in which:

FIG. 1 is a front elevational view of a prior art apparatus for carryinga cutting torch to move with a continuous cast steel strand;

FIG. 2 is a general schematic illustration of a prior art method ofcutting a still strand;

FIG. 3 is a front elevational view of a steel cutting apparatusincorporating a preferred embodiment of the invention;

FIG. 4 is a schematic illustration of a steel cutting method inaccordance with the invention;

FIG. 5 is a front elevational view of a steel cutting apparatus inaccordance with another embodiment of the present invention; and

FIG. 6 is a partial front elevational view of a steel cutting apparatusin accordance with a further embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIGS. 1 and 2, a conventional steel billet cutting apparatus10 is adapted to mount a cutting torch 12 for movement with an advancingcontinuous steel strand 14 (reference numeral 14 hereinafter indicateseither a steel strand, billet, bloom or small slab, whichever isappropriate). The apparatus 10 includes a pair of downwardly dependingframes 16, which are pivotally connected together by a pivot pin 18 thatact as a pair of clamp arms. A hydraulic cylinder 20 pivotally connectsthe respective upper ends 22 of the frames 16, in order to move clampingmembers 24 of the frames 16 into clamping engagement with vertical sidesof the steel strand 14. The apparatus 10 is mounted for movement along astationary guide track (not shown), which extends parallel to thelongitudinal axis of the steel strand or billet 14. When the frames 16clamp the steel strand 14 between the clamping members 24, the advancingsteel strand 14 moves the apparatus 10 along the stationary guide track.A cutting torch 12, shown in FIG. 2, is movable transversely across thesteel strand 14 as indicated by arrow 28 and thereby cuts the strand 14into billets. The transverse movement of the torch 12 is driven by adrive mechanism (not shown), which is adapted to mount on the frames 16of the apparatus 10, so that the apparatus and the attached cuttingtorch 12 are maintained in a fixed longitudinal position relative to themoving steel strand 14, so that the cutting torch is moved over thesteel strand 14 to sever the billet.

As the cutting flame 30 cuts through the strand 14, as shown in FIG. 2,molten steel and iron oxide flow downwardly between the faces 32 (onlyone of which is shown in FIG. 2) of the steel that define a kerfproduced by the cutting flame 30. Some of the molten material adheres toand forms slag beads 34 along the lower cut edges 36.

FIG. 3 illustrates a steel billet cutting apparatus 40 in accordancewith an embodiment of the invention. Apparatus 40 is mounted to theframe 16 shown in FIG. 1, the parts of which are indicated by the samereference numerals and are therefore not described. The apparatus 40includes a track 42 forming an arcuate path 44, shown in FIG. 4. Thetrack 42 is mounted at one end thereof by a mounting plate 46 to one ofthe frames 16, adjacent to the lower end 26 of the frame 16 and abovethe strand 14, which is clamped between the frames 16.

As shown in FIG. 4, the arcuate path 44 formed by the track is generallyone quarter of a circular path having its center located at a fixedpoint at which a cutting flame of the torch is continuously aimed. Inthis example, the center of the circular path is located at a rightside, bottom corner 48 of the strand 14. The arcuate path 44 defines aplane perpendicular to a longitudinal axis of the strand 14. The cuttingtorch 12 (FIG. 3) includes a mechanism for guiding the cutting torch 12along the track 42. For example, rollers (not shown) operatively engagethe track 42. Thus, the cutting torch 12 is adapted to move, as shown inFIG. 4, from the right side 50 of the strand 14 to the left side 52,while gradually rotating from a first orientation 54 perpendicular tothe bottom surface 56, to a second orientation 58 parallel to the bottomsurface 56 of the strand 14, the bottom surface 56 extending along ahorizontal plane. As the cutting torch 12 moves in the arcuate path 44,the cutting flame 30 is always aimed at the right side, bottom corner 48of the strand 14 and the molten material thereby flows towards theright-side bottom corner 48. The rate of movement of the cutting torch12 is dependent on a thickness of the steel, the characteristics of thecutting torch nozzle, the type of fuel and other factors well known inthe art. The cutting torch 12 is preferably moved at a predeterminedrate required to cut the steel most efficiently. Cutting the steel usingthis method results in a very small amount of slag forming on andadhering to the bottom corner 48 of the billet 14, rather than thesignificant amount that forms along the entire lower cut edge 56, asshown in FIG. 2.

Other steel products, for example, blooms and small slabs, whichgenerally have rectangular or square cross-sections, can also be cut inthis manner to reduce slag adherence. The apparatus 40 may also be usedto cut steel that has a non-rectangular cross-section. The cut can beeffected by aiming the cutting flame 30 at a fixed point defined by abottom corner of an imaginary square or rectangle drawn around thestill. In certain instances, efficiency may be increased if the lengthof the arcuate path 44 is greater than one quarter of a circular arc, aswill be understood by those skilled in the art. Interchangeable tracks42 having different radiuses are preferably used to cut respective sizesof steel, in order to keep the path traveled by the cutting torch 12 asshort as possible for any given cutting operation.

The cutting torch. 12 is moved by a drive mechanism operativelyconnected to the cutting torch 12 and preferably mounted to the sameframe 16 to which the track 42 is mounted. In the embodiment shown inFIG. 3, the drive mechanism includes a sleeve 60 having internal threads(not shown) rotatably connected to the cutting torch 12 at an axisindicated by a “+” 62. The axis 62 is positioned perpendicular to boththe plane determined by the track 42 and a threaded axial bore throughthe sleeve 60. The drive mechanism further includes a drive shaft 64having a free end and an end connected by means of a universal joint 66to a rotation-output shaft 68 of a gear box 70. The drive shaft 64 hasexternal threads for threadingly engaging the internal threads in theaxial bore of the sleeve 60, so that rotation of the rotation-outputshaft 68 moves the sleeve 60 along the drive shaft 64. As the sleeve 60is moved along the drive shaft 64, the drive shaft 64 pivots about anaxis 72 that extends through the universal joint 66. Movement of thesleeve 60 urges the cutting torch 12 along the track 42. The gear box 70is coupled to an electric motor 74, which controllably reciprocates thecutting torch 12 along the track 42. The gear box 70 and the electricmotor 74 are mounted to the frame 16 to which the track 42 is mounted bya mounting plate 76. The drive mechanism and the track 42 do notinterfere with the clamping action of the frames 16 because they aremounted to only one side of the frames 16.

In operation, the apparatus 40 is moved along the guide track (notshown) to a predetermined start position while the hydraulic cylinder 22is retracted to maintain the pair of frames 16 in an open position. Acontinuous steel strand 14 exiting from a caster (not shown) advancesbetween the open frames 16. When a predetermined length of the steelstrand 14 has advanced beyond a point aligned with the cutting torch 12,the hydraulic cylinder 20 is extended to close the pair of frames 16,thereby clamping the steel strand 14 between the two clamping members24. At this stage, the cutting torch 12 is preferably positioned at atop end of the track 42 and is oriented substantially vertically, asshown in FIG. 3. The apparatus 40 moves forward with the continuoussteel strand 14, and the electric motor 74 begins to rotate the driveshaft 64, thereby urging the cutting torch 12 along the track 42 whilethe cutting torch 12 is operated to produce a cutting flame 30, aimed atthe right-side, bottom corner 48 of the steel strand 14 to begin thecutting operation. When the cutting operation is completed, the cuttingtorch 12 has reached the other end of the track 42, where it is orientedin a substantially horizontal position. The hydraulic cylinder 20 isagain retracted to open the frames 16, and the apparatus 40 is movedback to the predetermined start position. Meanwhile, the electric motor74 rotates the drive shaft 64 in the opposite direction, thereby movingthe cutting torch 12 along the track 42 and back to its start positionin preparation for the next cutting operation.

FIG. 5 illustrates another embodiment of the invention, in which a steelcutting apparatus 80 is similar to the apparatus 40, shown in FIG. 3.The parts of the apparatus 80 which are identical to those of apparatus40 shown in FIG. 3 are indicated by the same reference numerals and arenot described. A drive-mechanism for the apparatus 80 includes a doubleacting fluid cylinder 82, which urges the cutting torch 12 along thetrack 42. The fluid cylinder 82 may be a pneumatic cylinder or ahydraulic cylinder. The cylinder 82 is pivotally connected to a supportstructure 84 about an axis 86 perpendicular to the plane determined bythe track 42. The support structure 84 has a first leg mounted to alower portion of the frame 16 and a second leg mounted to an upperportion of the same frame 16, for example, by a mounting plate 88. A ramof the cylinder 82 is pivotally mounted to the cutting torch 12 about anaxis 90, which is perpendicular to the plane determined by track 42.When the cylinder 82 is operated to extend the ram, the cutting torch 12is urged from the start position at the top end of the track 42, asshown in FIG. 5, to move along the track 42 to the end position, whereit is disposed in a substantially horizontally, as described above. Whenthe cylinder 82 is operated to retract the ram, the cutting torch 12 ismoved back to the start position.

Another embodiment of the invention is schematically illustrated in FIG.6, in which a steel cutting apparatus 100 is similar to the apparatus 40shown in FIG. 3. The parts of the apparatus 100 which are identical tothose of apparatus 40 shown in FIG. 3 are indicated by the samereference numerals and are not described. Some of the parts of theapparatus 10 shown in FIG. 1 are omitted from FIG. 6 in order to moreclearly illustrate the differences between the apparatus 100 andapparatus 40. The drive mechanism of the apparatus 100 converts movementof the frames 16 along the guide track (not shown) into rotationalmovement of a rotating shaft 102, which is rotatably supported, forexample, by one or more pillow blocks 104, on the frame 16 to which thetrack 42 is mounted. The rotating shaft is operatively connected to thedrive shaft 64 by the universal joint 66. The gear box 70 (FIG. 3) mayalso be included in the drive mechanism. A pinion 106 is affixed to therotating shaft 102 and is adapted to rotate together therewith. A rack108 is mounted to a stationary support, which, for example, may be theguide track for the movement of the apparatus 10. The pinion 106 engagesthe rack 108 and rolls along the rack 108 as the apparatus 10 is movedalong its guide track. The rotational movement of the pinion 106, whichdrives the rotating shaft 102, rotates the drive shaft 64, so that thesleeve 60 is urged along the drive shaft 64, causing the cutting torch12 to move along the track 42. As will be understood by those skilled inthe art, a mounting-linkage (not shown) may be required to keep thepinion 106 in engagement with the rack 108 when the frame 16 is releasedfrom the continuous strand 14 and returned to the start position. Themounting linkage may be incorporated into mounts for the rotating shaft102 or the rack 108, or both.

As described above, after the cut is completed using the apparatus 100,the hydraulic cylinder 20 is retracted to release the clamping members24 and the frame 16 is moved back to the starting position to beginanother cut. As the frame 16 is moved back to the starting position, thelinkage mechanism (not shown) keeps the pinion 106 engaged with the rack108 and rotation of the rotating shaft 102 returns the torch 12 to thestart position at the top of the guide track 42.

Modifications and improvements to the above-described embodiments of theinvention may become apparent to those skilled in the art. For example,although the apparatus has been described with reference to the cuttingof continuous cast strands, the apparatus described with reference toFIGS. 3 and 5 may likewise be used to cut stationary steel billets,slabs or beams. For stationary cutting applications, the apparatus 40,80may be mounted to a stationary base and the steel to be cut may be movedinto position under the guide track 42 using any one of many known heavymaterial manipulation mechanism Alternatively, the apparatus 40,80 maybe mounted to a mobile base that is rolled or driven into position oversteel to be cut.

The foregoing description is therefore intended to be exemplary ratherthan limiting. The scope of the invention is therefore intended to belimited solely by the scope of the appended claims.

I claim:
 1. A method of cutting steel with a cutting torch to reduceslag adherence to a cut edge of the steel, comprising steps of:commencing a cut at a first side of the steel; moving the cutting torchin an arcuate path shaped to continuously aim a cutting flame of thecutting torch at a fixed point located at a bottom of the first side ofthe steel; and following the arcuate path to keep the cutting flameaimed at the fixed point until the steel is cut.
 2. A method as claimedin claim 1 further comprising steps of moving the cutting torchtransversely relative to the steel, while maintaining the cutting torchstationary relative to a longitudinal axis of the steel.
 3. A method asclaimed in claim 1 further comprising steps of synchronously moving thecutting torch and the steel in a direction parallel with a longitudinalaxis of the steel, while moving the cutting torch transversely relativeto the steel along the arcuate path.
 4. A method as claimed in claim 1further comprising a step of returning the cutting torch to a startingposition after the steel is cut.
 5. A method of cutting steel billetsfrom a continuous cast steel stand to reduce slag adherence to a cutedge of the billets, comprising steps of: commencing a cut at a firstside of the steel strand; moving the cutting torch in an arcuate pathshaped to continuously aim a cutting flame of the cutting torch at abottom corner of the first side of the steel strand; and following thearcuate path to keep the cutting flame aimed at the bottom corner untilthe steel strand is cut to form the steel billet.